If you read the Indian Ponds Association (IPA) newsletter, that covers news about Mystic Lake, Middle Pond, and Hamblin Pond in Marstons Mills, you will see the headline, “Everything is Go for Mystic Lake Alum Treatment.”

The lake needs some help to recover from phosphorus pollution whose source we might not think of in the 21st century. Not lawns. Not golf courses. Not septic systems.

Farming holds the smoking gun. And a dose of alum – due to be administered soon after Labor Day – has been prescribed as the cure.

A paper written and provided by Holly Hobart, president of the IPA, notes that the northern shore of Mystic Lake hosted “intensive agricultural operations. There was a large dairy farm for 40 years, also another farm that grew prize-winning fruits, vegetables, pigs, and cranberries,” Hobart wrote.

To this day, there is a now-unused cow tunnel under Race Lane, which Hobart’s paper says allowed “as many as 150 cows” to reach drinking water. Each cow, Hobart wrote, could produce a hundred pounds of manure a day, full of phosphorus.

The cow manure, and other household and agricultural waste, “added a great deal of phosphorus…deposited in years past and released from the sediments under summertime conditions of reduced oxygen in the deepest parts of the pond, that is causing algae blooms in Mystic Lake today,” Hobart wrote. The blooms are killing fish and mussels that are native to the lake.

“The permit for alum was hard-won,” said Rob Gatewood, the town’s conservation administrator, because of what he called a “sensitive habitat” that includes rare species of mussels. “The mussels will rebound” in Mystic Lake, “and that’s what we’re after,” said Gatewood.

What the alum does to help the lake is to bind with the phosphorus into an insoluble compound that sinks into the sediment and cannot redissolve, according to several sources.

Alum, also known chemically as aluminum sulfate, has been used “since the time of the Romans” to purify water, said Hobart, and once it has done its work in Mystic Lake it will leave no residue, she said.

Mystic Lake is “a very big and a very deep pond,” said Carl Thut, vice president of the IPA and a chemist with a Ph.D. “The beauty of alum,” he said of the mineral as a cure for the algae bloom that is killing the native fish and mussels, “is that it’s permanent.”

Hobart added that the alum treatment will not harm the three species of mussels in the lake that are considered “endangered.” Seven species live in Mystic Lake, but four are not “listed” as threatened with extinction, she said.

Some Mills residents still have doubts about the project, questioning the effectiveness and cost of the treatment selected.

According to information provided by the IPA, the town has awarded a contract for the alum treatment to Aquatic Control Technology of Sutton, and AECOM, which the IPA literature says “conducted the design and permitting phase” of the alum project in 2008.

The Indian Ponds Association, Inc., has scheduled its annual meeting for July 11 at 4 p.m., and its featured presentation will be by the Alum Working Group, which consists of Thut, Hobart, Gatewood, past IPA president Emory Anderson, and Bob Nichols.

The business meeting will also include the presentation of the Edward Schwarm scholarship to BHS senior Nicholas Atcheson, an Eagle Scout who has worked on Indian Ponds beaches projects and who plans to attend Westfield State College to major in criminal justice and participate in the Honors program. IPA publicity says that Atcheson intends to return to Barnstable as a police officer and later serve with the FBI.

Schwarm was an engineer and former IPA director who, with his wife Erla, retired to Marstons Mills. Both died in 2005. Edward Schwarm, according to his family, served on the team that saved the Apollo 13 mission from imminent death by helping to design a way for the crew to breathe oxygen from the unused lunar excursion module.

The Web site for the Indian Ponds Association, Inc., is indianponds.org. The association can also be reached at POB 383, Marstons Mills MA 02648.